Vacuum degassing unit

ABSTRACT

A vacuum degassing unit comprising a reservoir vessel, a pivot structure for mounting said vessel, a degassing vessel having a pair of siphon legs extending into said reservoir vessel, means for maintaining a liquid contained within said reservoir vessel at differential levels respectively relative to said siphon legs to maintain a siphoning flow therethrough, and means for tilting said reservoir vessel about said pivot structure for initiating said siphoning flow.

United States Patent Anderson et al.

[54] VACUUM DEGASSING UNIT [72] Inventors: C. H. Anderson, MacMurray, Pa.;

Colin Griffiths, Arlington Heights,

[73] Assignee: Pullman Incorporated, Pittsburgh,

[22] Filed: April27,1971

[211 App]. No; 137,797

[52] US. Cl. ..'.266/34 v, 75/49 [5| 1m. Cl ......C 2lc 7/10 [58] Field of Search ..75/49; 13/3 l; 266/34 v, 13

[56] References Cited UNITED STATES PATENTS 3,201,224 8/1965 Grim ..75/49 3,215,423 ll/1965 Taylor ..266/34 V Dec. 19, 1972 3,572,671 3/1971 Worner ..266/34 V I FOREIGN PATENTS OR APPLICATIONS 02,588 l/l965 Canada ..266/34 V Primary Examiner-Gerald A. Dost Alt0rneyBucll, Blenko & Ziescnheim [57] ABSTRACT A vacuum degassing unit comprising a reservoir vessel, a pivot structure for mounting said vessel, a degassing vessel having a pair of siphon legs extending into said reservoir vessel, means for maintaining a liquid contained within said reservoir vessel at differential levels respectively relative to said siphon legs to maintain a siphoning flow therethrough, and means for tilting said reservoir vessel about said pivot structure for initiating said siphoning flow.

14 Claims, 3 Drawing Figures d i i l llllllllll] lllllllllll Illllllllll PATENTEDHEI: 19 I972 SHEEI 1 0F 3 A ENTEMEB 19 I972 3106,4453

sum 2 0F 3 Inventors C.H. Anderson 8 Colin Griffiths f m /zzim' 66%! W VACUUM DEGASSING UNIT The present invention relates to a vacuum degassing unit and more particularly to a unit of a character described which can be employed with high temperature liquid metals and which is provided with means for facilitating a siphoning operation within the unit.

Although our invention is described with reference primarily to liquid metals, its application to other liquids, particularly under-conditions of high volumetric flows at elevated temperatures, will be obvious.

- in vacuum treatment techniques, the molten metal is exposed to a very low gas pressure,,which, as is well known, facilitates the removal of gases and volatile impurities from the liquid metal. In the most simple conventional apparatus utilized in vacuum treatment, the molten metal is contained in an open top vessel and a sealed enclosure is placed around the vessel. The vessel is heated while the atmosphere within the enclosure is evacuated to maintain a very low ambient pressure of the molten metal. As is well known, this simple treatment apparatus has two rather glaringdisadvantages in that'the purification action is vary slow and the process is not continuous. These disadvantages can be mitigated to some extent by agitating the molten metal contained within the open vessel, for example in the manner disclosed by the-Taylor patent noted below, and by providing the surrounding enclosure with pressure locks to facilitate batch changes.

There are, of course, knownforms of vacuum degassing apparatus which are capable of operating on a continuous basis. For the most part, such apparatus involves some form of siphoning system with complicated means for initiating the siphoning action or for enhancing the siphoning flow. The problems involved in establishing and maintaining the siphoning flow are, of course, compounded from the considerable weight of the liquid metal and its usually elevated temperature. Rigidized supporting and containing structures, refractory linings, and the like are required which in the past have been unduly complicated. The complexity of known degassing units have not only limited their applicability to specific, usually lower temperature liquid metals, but also have limited their productivity. Finally, previous degassing units have not been provided with adequate means for tapping off an overlying slag. layer or the like, nor for. adequately defining suitable differential liquid metal levels, which are prerequisite to an optimum siphoning flow. Previous degassing units have not been capable of close association with a melting and preliminary purification facility for the molten metal, such that the metal can be delivered rapidly and continuously to the degassing unit.

Examples of the prior art, which has been briefly described above are found in the US. Patents to Hart, US. Pat. Nos. 3,402,921; Armbruster, 3,310,850; Taylor, 3,235,243; Miller, 3,212,767; and Williams 1,921,060. While each of these references is admirably suited to a solution of particular problems, none of these references is adaptable both to high volume production contemplated by the present invention and to the very high. temperatures of certain molten metals, such as liquid steel. For example, the flow of liquid metal through the Hart apparatus is drop-wise as illustrated although the Hart apparatus is continuous on this basis. Similar apparatus is shown in the Williams and Miller patents, which, however, appear to be batch operations. The Armbruster patent is directed to means for facilitating the siphoning operation solely by the injection of inert gas into the incoming siphon leg. The Taylor patent relates to an open vessel and surrounding enclosure, together with means for agitating the liquid metal.

We overcome these disadvantages of the prior art by providing a tiltable and partitioned reservoir vessel which is capable of receiving a large through-put of liquid metal and which can be fed continuously by a suitable melting facility, for example, a pair of relatively large electric furnaces. The furnaces also are tiltably mounted, in accord with our invention, to facilitate tapping directly into the reservoir vessel. A degassing vessel is provided for siphoning molten metal from one of the reservoir compartments and returning it to another. The tiltable arrangement of the reservoir facilitates tapping'the furnaces associated therewith and any slagging operation that may be desired to be carried out. Tilting of the reservoir also facilitates initiation and maintenance of the siphon flow and the withdrawal of molten slag and degassed metal respectively from differing outlets of the reservoir. Another feature of our invention involves mounting the degassing vessel directly on the reservoir vessel for tilting movement therewith in further control of the siphoning flow. Means are also associated with the tiltable reservoir and the degassing vessel for preheating the reservoir vessel and/or the degassing vessel to receive liquid metal and/or to maintain the liquid metal at a given temperature. The reservoir vessel is furnished withunique means for determining optimum differential liquid levels therein for a maximum siphoning characteristic. The aforementioned partition is orificed to facilitate filling and draining of the reservoir. The degassing vessel is constructed in a rather unique manner pertinent to its relationship with the reservoir vessel when mounted thereon and to its handling of both high temperature liquid metal and off-gases.

- We accomplish these desirable results by providing a vacuum degassing unit comprising a reservoir vessel, a pivot structure for mounting said vessel, a' degassing vessel having a pair of siphon legs extending into said reservoir vessel, means for maintaining a liquid contained within said reservoir vessel at differential levels respectively relative to said siphon legs to maintain a siphoning flow therethrough, and means for tilting said reservoir vessel about said pivot structure for initiating said siphoning flow.

We also desirably provide a similar vacuum degassing unit wherein said degassing vessel is mounted on said reservoir vessel for tilting movement therewith.

We also desirably provide a similar vacuum degassing unit wherein said degassing vessel is mounted on a partition structure within said reservoir vessel for tilting movement with said reservoir vessel.

We also desirably provide a similar vacuum degassing unit wherein said degassing vessel is sealed for maintenance of a vacuum therein and has an end portion shaped for insertion through a closely fitting opening in said reservoir vessel for engagement with supporting means therefor within said reservoir vessel.

We also desirably provide a similar vacuum degassing unit wherein said differential level maintaining means include in addition an outlet port for each compartment, the lowermost areas of said ports being disposed at differing elevations to define said differential liquid levels.

. We also desirably provide a similar vacuum degassing unit wherein said reservoir vessel is provided with inlet port means, at least one melting furnace is mounted adjacent said'inlet port means, and means are provided for pivotally mounting said furnace and for tilting'said furnace'about said pivot mounting to a tapping position relative to said inlet port means.

. During the foregoing discussion, various objects, features and advantages of the invention have been set forth. These and other objects, features and advantages of the invention together withstructural details thereof will be elaborated uponduring the forthcoming description of certain presently preferred embodiments of theinvention and presently preferred methods of practicing the same. v i

In the accompanying drawings I have shown certain presently preferred embodiments of the invention and have illustrated certain presently preferred methods of practicing the same,'wherein:

FIG. 1 is a top plan view of one form of vacuum degassing unit, including in this example a melting facility, and arranged in accordance with my invention; FIG. 2 is a vertically and longitudinally sectioned view of the 'apparatus'as shown in FIG. 1 and taken generally along reference line IIll thereof; and

1 FIG. 3 is a right end elevational view of the apparatus as shown in FIG. 1.

Referring now more particularly to the drawings, an exemplary vacuum degassing unit is'illustrated in conjunction with a pair of melt furnaces 12, 14 furnished in this example in the form of electric furnaces arranged for tapping directly into reservoir vessel 16" forming part 'of the vacuum degassing unit 10. Each of the electric furnaces 12, 14 includes a removable roof structure 18, electrodes 20 and generally circular containment vessel or enclosure 22, all of which can be constructed, except as noted below, along the lines of conventional configurations. The roofs 18 of the furnaces l2, l4 desirably are made removable, together with the electrodes 20, for charging purposes in accord with conventional techniques. Alternatively, the roofs 18 and electrodes 20, together with exhaust duct work (not shown) can be'supported and manipulated in accordance with the invention described and claimed in a copending, coassigned application of Leslie A. Chermely, Ser. No. 672,321, filed Oct. 2, 1967 entitled LIFTING ARRANGEMENT FOR A FURNACE FUME ELBOW AND THE LIKE.

Each electric furnace 12 or 14 is further provided with a pouring spout 24 to facilitate tapping the furnace directly into the reservoir vessel 16, which is described in detailbelow. In furtherance of this purpose, each furnace vessel 22 is provided with a pair of lugs 26 disposed in this example generally on either side of the associated pouring spout 24 (FIG. 1). Each lug 26 is pivoted at 28 (FIG. 3) to a heftily constructed supporting clevis 30, and the clevises 30 are capable of sup porting substantially the entire weight of the furnace 12 or 14, when loaded to design capacity.

Diametrically opposite from the pivots 28, each furnace enclosure 22 is supported by a pair of hydraulic cylinders 32, the distal piston ends of which are pivoted 22. Each cylinder 32 is pivoted M38 and is sufficiently elongated outwardly therefrom (relative to the furnace enclosure 22) to tilt the associated furnace vessel 22 from its solid outlined operating position as shown in the several figures to its tapping position, represented in FIG. 3 by the chain-outlined position 40 of the furnace 14.

At the tapping position 40 tapping cylinder 42 is actuated to open a tapping port in the associated spout 24 through suitable-linkage including arm 44. In order to permit tilting of each furnace vessel 22 to its tapping position 40, the electrodes 20 and roof structure 18 are raised and then swung aside either by conventional equipment or by the novel arrangement set forth in the aforementioned Chermely application. I

The reservoir vessel 16 is supported fora similar tilting operation, for drainage purposes and for initiation of the siphoning operation as described below but is provided with dual pouring ports 48, 50 in-the end'portions respectively of the vessel 16. In the illustrated arrangement, then, the reservoir vessel 16 is tiltable from an operating position represented by its solid outlines in'the several Figures to a first pouring position 52 for draining into a product ladle 54 and to a second pouring position 56 for draining in this example into a slag or overflow ladle 58. The slag ladle 58 is provided with lifting lugs 59 to permit insertion and withdrawal of the ladle 58 by an overhead-crane or the like. The ports 48, 50 in cooperation with partition structure 92 described below determine the differential liquid levels in the compartments 88, 90 likewise described below.

The product ladle 54 for facile maneuverability is mounted upon a wheeled vehicle 60 having in this example railway trucks 62 for engagement with tracks 64. The tracks 64 together with the ,ladles 54, 58 are mounted in a service compartment 65 generally below the floor structure 66 of the plant so as to clear the reservoir vessel 16 and the transformer enclosures 68 associated with the furnaces l2, l4.

Tilting of the reservoir vessel 16 to the aforementioned drainage positions 52, 56 and, of course, its in termediate operating position as shown is effected by means of a trunnion or pivot structure including shaft 70, a number of vessel lugs 72 notched for engaging the shaft and pivot support 74 having a number of cleats 76 thereon and interleaved with the vessel lugs 72 for engaging and supporting the pivot shaft 70. Tilting of the reservoir vessel 16 is controlled by means of hydraulic cylinder 78 whose distal piston end is pivoted to bracket 80 secured to the undersurface of the vessel 16. Both the pivot structure 70-76 of the vessel 16 and its tilt cylinder 78 are located beneath the floor structure 66 within the aforementioned compartment 65.

When the vessel 16 is tilted to its drainage position 52, a curving splash shield 80 is affixed to the floor structure 66 for the protection of operating personnel and thesurrounding equipment. The splash shield is furnished with an opening 82 to accommodate the adjacent end of the vessel 16 during its tilting maneuver.

In addition to its outlet ports 48, 50, the reservoir vessel 16 is provided with a pair of inlet port structures 84, 86 (FIGS. 1 and 3) which are disposed generally in alignment with the pouring spouts 24 of the furnace enclosures 22, in the solid outlined or operating position of the reservoir vessel 16. The furnaces 12, 14 are tilted for tapping directly into the reservoir vessel inlets 84, 86 respectively as described above.

The vessel 16 is further provided with refractory top, side and bottom wall structures (FIGS. 1 and 2) and is divided internally into feed and outlet compartments 88, 90 respectively by a partition structure 92. The partition structure 92 is provided with a relatively small orifice 93 adjacent the bottom edge of the partition 92 to facilitate initial filling and final draining of the reservoir vessel 16 and its compartments88,'90. A top wall structure 94 of the vessel is provided in this example with a circular opening 96 centered generally over the partition structure 92. Desirably, the partition 92 and the opening 96 likewise are centered over the vessel pivot or trunnion shaft 70 (FIG. 2) to afford optimum support to a degassing vessel 98 which is mounted, in the .illustrated example upon the partition structure 92. A lower end portion of the vessel 98 is shaped for closely fitted insertion through the top wall opening 96, of thereservoir vessel. To minimize heat losses between the degassing and reservoir vessels, a sealing flange 100 is secured to the outer periphery of the degassing vessel 98 and is shaped to confine a sealing ring 102 between the flange 100 and the juxtaposed surfaces of the top wall 94 of the reservoir vessel 16.

The degassing vessel 98 further includes a lower molten metal chamber 104 and a gas .bonnet 106. 'In this example the walls of the chamberl04 and the partition structure 92 preferably include refractory brick or other high-temperature resistant material. The gas bonnet 106 can be provided in this example with a relatively thinner refractory lining 108 and further includes an exhaust duct 110 for removing gases and volatile material eliminated from the molten steel or other high temperature liquid contained within the refractory chamber 104. Desirably, the bonnet 106 also includes a burner port 112 through which a gas or oil fired burner structure (not shown) of conventional nature can be inserted 'for start-up purposes or whenever additional heat must be supplied to the molten metal contained within the chamber 104. For the same purpose, the top wall 94 of the reservoir vessel 16 is similarly provided with a burner port 114 disposed generally over the purified metal or outlet compartment 90 of the reservoir vessel 16. On the other hand, the top wall structure 94 includes in this example both a burner port 116 with burner 118 therein and disposed generally over the inlet or feed compartment 88 of the vessel 16. The burner 118 is turned on during the operation of the vacuum degassing unit in order to maintain the temperature of the metal tapped into the reservoir vessel 16 from one of the electric furnaces 12, 14.

The degassing vessel 98 is further provided with a pair of siphon legs 120, 122 extending from the bottom wall 1280f its refractory section 104 and communicating with siphon compartment 124 enclosed therein. The siphon legs 120, 122 extend in this example nearly to bottom wall structure 126 (FIG. 2) of the reservoir vessel 16 and straddle the partition structure 92.

As mentioned more generally heretofore, the commencement of the siphoning action in previous degassing units has long posed a number of difficult problems. We eliminate the problems associated with initiating the siphoning flow by spatially associating the bottom wall structure 128. of the siphon compartment 126 and correlating this arrangement with the tilt angle of the reservoir vessel in its forward tilted position 52 such that the molten metal 130 contained in the inlet compartment 88 of the vessel 16 flows into the siphon compartment 126 through incoming siphon leg 120 and thence into the outlet compartment through outgoing siphon leg 122. The level of molten metal 132 within the outlet compartment 90 as defined by the lowest elevation of the product tapping port 50, is maintained lower than that of the liquid metal 130 within the feed compartment 88 as determined by the lowest elevation of its tapping port 48 (FIG. 2). Thus, a continuous flow of liquid steel or other molten metal from the feed compartment 88 through the siphon compartment 1260f the degassing vessel 98 to the outlet compartment 90 is maintained. This siphoning flow,

which of course passes through the interconnecting,

siphon legs 120, 122, provides the necessary agitation to the liquid metal 134 contained within the siphon compartment 126 for quick removal of the dissolved gases and other volatile materials contained within the molten metal under the conditions of partial vacuum maintained within the degassing chamber 98 by means of a suitable and conventional blower or compressor (not shown) coupled to the exhaust duct of the vessel 98. I

In conjunction with the tilting capability of the vessel 16, an inert gas can be injected through suitable means (not shown) directly into the ingoing siphon leg for a further increase in the flow of molten metal therethrough. Similarly an induction coil can be coupled to the ingoing siphon leg 120 to likewise increase the siphoning flow.

In addition to its function in initiating the siphoning flow, the tilting capability of the vessel 16 to its chain outline positions 52 and 56 embody other features of our invention. For example, the tilting capability facilitates filling and draining compartments 88, 90 of the reservoir vessel, and permits modification of the differential liquid levels to meet various operating conditions. ln addition,'an overlying slag layer on the liquid metal contained within the feed compartment 88 can be skimmed off into the ladle 58, when such slag is received from either one of the electric furnaces 12,14 or whenever it is desired to add slagging materials to the liquid metal 130 in the feed compartment 88 for further purification purposes.

In operation, a charge is introduced into one or both of the furnaces 12, 14 which is then heated by electric currents in the secondary circuit, including bus-bars and the aforementioned electrodes 20, of transformer 136 or 138. When the charge is' ready for tapping, the associated furnace 12 or 14 is tilted by means of its tilt cylinder 32 to tap the melt into the feed chamber 88 of the reservoir vessel 16 through its inlet port 84 or 86. While the molten metal is contained within the feed compartment 88, a pre-determined temperature thereof is maintained by operation of the burner or other heat transferring means 118. The burner 118 is supplied with flexible lines denoted generally at 142 to permit operation of the burner 118 when the vessel 16 is tilted to initiate the siphoning flow. With tilting of the vessel 16 generally toward its tilted position 52 (FIG. 2) molten metal flows through l060l l 0009 the incoming siphon leg 120 to findits level in the siphon compartment 126 of the. degassing vessel 98. Thence, the liquid metal flows downwardly through outgoing siphon leg 122 into the outlet compartment 90 of the reservoir vessel 16. The vessel 16 is then returned to its substantially level operating position, whereupon the siphoning flow is .maintained by the differential liquid levels in the. feed and outlet compartments 88, 90 and bythe absence of dissolved gases and other light componentsin the purified liquid metal descending through the outgoing siphon leg 122.

As each ingot mold or ladle 54 is filled by the continuous operation of the degassing unit 10, another ingot mold or ladle 54 is wheeled into position at the product outlet port 50 of the reservoir vessel 16. The succeeding molds or ladles 54' can be moved on their carriages 60 by suitable and conventional traction means (not shown).

From the foregoing it will be apparent that novel and efficient forms of Vacuum Degassing Unit have been described herein. While I have shown and described certain presently preferred embodiments of the invention and have illustrated presently preferred methods of practicing the same it is to be distinctly understood that the invention is not limited thereto but may be otherwisevariously embodied and practicedwithin. the spirit and scope of the invention.

We claim:

l. A vacuum degassing unit comprising a reservoir vessel, a pivot structure for mounting said vessel, a degassing vessel having a pair of siphon legs extending into said reservoir vessel, means for maintaining a liquid contained within said reservoir vessel at differential levels respectively relative to said siphon legs to maintain a siphoning flow therethrough, and means for tilting said reservoir vessel about said pivot struc ture for initiating said siphoning flow.

2. The combination according to claim 1 wherein said degassing vessel is mounted on said reservoir vessel for tilting movement therewith.

3. The combination according to claim 1 wherein said differential level maintaining means include a partition structure separating the interior of said reservoir vessel into compartments, said partition structure being interposed between said siphon legs. I

4. The'combination according to claim 2 wherein said degassing vessel is mounted on a partition structure within said reservoir vessel for tilting movement with said reservoir vessel.

5. The combination according to' claim 2 wherein said degassing vessel is sealed for maintenance of a vacuum therein and has an end portion shaped for insertion through a closely fitting opening in said reservoir vessel for. engagement with supporting means therefor within said reservoir vessel.

6. The combination according toclaim .5 wherein said supporting means and said degassing vessel are substantially centered over said pivot structure.

7. The combination according to claim 3'wherein said partition structure is provided with a relatively small orifice adjacent the bottom edge thereof and communicating with said compartments to facilitate filling and draining said reservoir vessel.

8. The combination according to claim 3 wherein said differential level maintaining means include in ad dition an outlet port foreach compartment, the lowermost areas of said ports being disposed at differing elevations to define said differential liquid levels.

9. The combination according to claim 1 wherein said reservoir vessel is provided with inlet port means, at least one melting furnace is mounted adjacent said inlet port means, and means are provided for pivotally mounting said furnace and for tilting said furnace about said pivot mounting to a tapping position relative to said inlet port means. I

l0. The combination according to claim 3 wherein said compartments include a feed compartment and an outlet compartmennsaid feed compartment includes a pair of generally opposite inlet port structures mounted on said reservoir vessel in communication with said feed compartment, a tiltable melting furnace is mounted adjacent each of said inlet port structures, and means are provided for pivotally mounting'each of said furnaces and for tilting said furnaces about their pivot mountings respectively to tapping positions associated respectively with said inlet port structures.

11. The combination according to claim 3 wherein said compartments include a feed compartment and an outlet compartment, and heat transferring means are mounted in a wall structure of said reservoir vessel in communication with said feed compartment for supplying heat to the liquid contained therein.

12. The combination according to claim 1 wherein said degassing-vessel includes a refractory siphon compartment and a gas bonnet mounted thereon.

13. The combination according to claim 12 wherein said gas bonnet includes means for evacuating the degassing vessel and a burner port for insertion of a burner structure for preheating said degassing vessel.

l4. The combination according to claim 5 wherein said degassing vessel includes a sealing flange shaped for juxtaposition to a wall structure of said reservoir vessel upon said insertion, and a sealing ring is com pressed between said flange and said wall structure. 

1. A vacuum degassing unit comprising a reservoir vessel, a pivot structure for mounting said vessel, a degassing vessel having a pair of siphon legs extending into said reservoir vessel, means for maintaining a liquid contained within said reservoir vessel at differential levels respectively relative to said siphon legs to maintain a siphoning flow therethrough, and means for tilting said reservoir vessel about said pivot structure for initiating said siphoning flow.
 2. The combination according to claim 1 wherein said degassing vessel is mounted on said reservoir vessel for tilting movement therewith.
 3. The combination according to claim 1 wherein said differential level maintaining means include a partition structure separating the interior of said reservoir vessel into compartments, said partition structure being interposed between said siphon legs.
 4. The combination according to claim 2 wherein said degassing vessel is mounted on a pArtition structure within said reservoir vessel for tilting movement with said reservoir vessel.
 5. The combination according to claim 2 wherein said degassing vessel is sealed for maintenance of a vacuum therein and has an end portion shaped for insertion through a closely fitting opening in said reservoir vessel for engagement with supporting means therefor within said reservoir vessel.
 6. The combination according to claim 5 wherein said supporting means and said degassing vessel are substantially centered over said pivot structure.
 7. The combination according to claim 3 wherein said partition structure is provided with a relatively small orifice adjacent the bottom edge thereof and communicating with said compartments to facilitate filling and draining said reservoir vessel.
 8. The combination according to claim 3 wherein said differential level maintaining means include in addition an outlet port for each compartment, the lowermost areas of said ports being disposed at differing elevations to define said differential liquid levels.
 9. The combination according to claim 1 wherein said reservoir vessel is provided with inlet port means, at least one melting furnace is mounted adjacent said inlet port means, and means are provided for pivotally mounting said furnace and for tilting said furnace about said pivot mounting to a tapping position relative to said inlet port means.
 10. The combination according to claim 3 wherein said compartments include a feed compartment and an outlet compartment, said feed compartment includes a pair of generally opposite inlet port structures mounted on said reservoir vessel in communication with said feed compartment, a tiltable melting furnace is mounted adjacent each of said inlet port structures, and means are provided for pivotally mounting each of said furnaces and for tilting said furnaces about their pivot mountings respectively to tapping positions associated respectively with said inlet port structures.
 11. The combination according to claim 3 wherein said compartments include a feed compartment and an outlet compartment, and heat transferring means are mounted in a wall structure of said reservoir vessel in communication with said feed compartment for supplying heat to the liquid contained therein.
 12. The combination according to claim 1 wherein said degassing vessel includes a refractory siphon compartment and a gas bonnet mounted thereon.
 13. The combination according to claim 12 wherein said gas bonnet includes means for evacuating the degassing vessel and a burner port for insertion of a burner structure for preheating said degassing vessel.
 14. The combination according to claim 5 wherein said degassing vessel includes a sealing flange shaped for juxtaposition to a wall structure of said reservoir vessel upon said insertion, and a sealing ring is compressed between said flange and said wall structure. 